The retinoblastoma gene product RB can regulate transcription in a positive or negative manner depending on the cell type through specific binding to transcription factors E2F or Elf-1. Sp1 activity is stimulated by RB but no interaction has been demonstrated. Moreover, RB has been shown to modulate transcription by a mechanism independent of E2F binding. Data from the PI's lab has suggested that RB may positively or negatively regulate transcription through interactions with promoter-specific, chromatin remodeling, or basal transcription factors. RB interacts specifically with the TBP-associated factor TAFII250 and the p89 subunit of TFIIH. Also, cyclin D1 can functionally interact with TAFII250 to regulate Sp1-mediated transcription. TAFII250 is important for regulation of G1/S specific genes, cell cycle and apoptosis, whereas TFIIH is involved in the release of RNA polymerase II from transcription initiation complex and in DNA excision repair. The main goal of this study is to determine how RB and cyclin D1 regulate transcription and/or other biological activities through interactions with TAFII250/TFIID and in the case of RB, p89/TFIIH. The experiments described in the proposal are expected to provide important insights into the mechanism of how RB and cyclin D1 function to regulate transcription directly, cell differentiation, and tumorigenesis.